The present invention relates to a method and a system of determining the location of an object in a medium having a permittivity substantially different to that of the permittivity of the object. More particularly, the present invention is concerned with a system for determining the depth of an object in the medium and/or a position on the surface of the medium closest to the object.
The location of objects, particularly metallic objects, in a medium such as the ground, using electromagnetic radiation, is a problem which has received much attention. Objects which lie within a medium and which have a permittivity which is different from that of the surrounding medium such that it will reflect the electromagnetic radiation. Typically the problem has been approached in the prior art by using pulsed radar systems in order to measure the propagation delay of the pulses travelling through the medium. Such systems are described in U.S. Pat. No. 3,775,765 and U.S. Pat. No. 3,806,795.
This technique however suffers from the disadvantage that in order to measure the depth of an object in the medium it is necessary to have some knowledge of the dielectric properties of the medium.
The problem of requiring knowledge of the dielectric properties of a medium has been avoided in U.S. Pat. No. 3,392,384 which discloses a technique for detecting the presence of an object in a medium. In this technique a pair of transmitting and receiving antennas are used to transmit electromagnetic radiation into the medium and receive electromagnetic radiation reflected from the object as well as undesired radiation reflected from the surface of the medium. In this technique the surface reflection is removed by comparing two channels. Although this arrangement does not require knowledge of the dielectric properties of a medium, it is unable to determine the depth of an object. The arrangement merely provides an indication of the presence of an object.
The object of the present invention is thus to provide a simple system for and a method of determining the position of an object in a medium without requiring knowledge of the dielectric properties of the medium or of the object.